It is a commonly known arrangement to provide a pressurised container or keg with a tubular neck-like socket (often called a Barnes neck), which is welded to the container. Valved closure units engage these sockets, and are arranged to seal and control the entry of carbon dioxide or other gas as a pressurising agent into the container, and the exit of beer or carbonated soft drinks via a separate dispense head. The closure units also permit the entry and exit of cleaning liquid and/or steam during the washing process of the container.
A typical closure unit for such a socket includes a bush which is received in the tubular neck and permits the filling, dispensing or retention of beer or carbonated soft drinks. The bush is made as a one-piece unit from metals such as stainless steel, aluminium, brass, etc., and is usually externally threaded at the upper end to engage a like-thread of the neck; the bush forms a valve seat at the other end.
A tubular member (retainer) is located below and supported by the valve seat. This tubular member houses two concentric valves, one being a gas valve and the other a beverage valve which are separately spring-loaded and act in association with a siphon tube, which extends into the container, and typically to near the bottom of the container to regulate the flow of the pressurising agent and beverage. A typical example of such is shown in U.S. Pat. No. 4,142,658 assigned to GKN Sankey Limited.
This known arrangement is generally satisfactory, however there are a number of disadvantages, and specifically that:
i) If the closure unit is to be removed and the bush is not unscrewed from the neck carefully it will eject with great force, and this action is potentially dangerous to a person servicing the container.
ii) Unauthorised removal or loosening of the valved closure unit may cause contamination of the beer or soft drink due to entry of micro-organisms; that is, the known closure units are not tamper-proof.
iii) The gas valve is a metal piece, tubular in shape having a radially outward extending flange on the upper end, and on which flange a mass of resilient material is applied to form a seal with the bush. During cleaning the entire valved closure unit is exposed to the action of pressurised washing liquid, and to heat from steam. Experience has shown that the gas valve needs to be replaced frequently due to damage which is caused by such cleaning procedure. That is, during cleaning the resilient material is hardened by steam and possible reaction to the washing liquid, and the contact of pressurised steam can cause the material to break, weaken, peel or dislodge, thereby resulting in the closure unit leaking and become non-functionable in subsequent use.